Buckminsterfullerene

Buckminsterfullerene is the most common naturally occurring fullerene. Small quantities of it can be found in soot. It also exists in space. Neutral has been observed in planetary nebulae and several types of star. The ionised form, , has been identified in the interstellar medium, where it is the cause of several absorption features known as diffuse interstellar bands in the near-infrared. ==History==

s have the same arrangement of polygons as buckminsterfullerene, . Theoretical predictions of buckminsterfullerene molecules appeared in the late 1960s and early 1970s. It was first generated in 1984 by Eric Rohlfing, Donald Cox, and Andrew Kaldor, using a laser to vaporize carbon in a supersonic helium beam, although the group did not realize that buckminsterfullerene had been produced. In 1985 their work was repeated by Harold Kroto, James R. Heath, Sean C. O'Brien, Robert Curl, and Richard Smalley at Rice University, who recognized the structure of as buckminsterfullerene. Smalley and team were able to use a laser vaporization technique to create carbon clusters which could potentially emit infrared at the same wavelength as had been emitted by the red carbon star. Hence, the inspiration came to Smalley and team to use the laser technique on graphite to generate fullerenes. Using laser evaporation of graphite the Smalley team found Cn clusters (where and even) of which the most common were and . A solid rotating graphite disk was used as the surface from which carbon was vaporized using a laser beam creating hot plasma that was then passed through a stream of high-density helium gas. The carbon species were subsequently cooled and ionized resulting in the formation of clusters. Clusters ranged in molecular masses, but Kroto and Smalley found predominance in a cluster that could be enhanced further by allowing the plasma to react longer. They also discovered that is a cage-like molecule, a regular truncated icosahedron. Another paper on the characterization and verification of the molecular structure followed on in the same year (1990) from their thin film experiments, and detailed also the extraction of an evaporable as well as benzene-soluble material from the arc-generated soot. This extract had TEM and X-ray crystal analysis consistent with arrays of spherical molecules, approximately 1.0 nm in van der Waals diameter The method was simple and efficient to prepare the material in gram amounts per day (1990) which has boosted the fullerene research and is even today applied for the commercial production of fullerenes. The discovery of practical routes to led to the exploration of a new field of chemistry involving the study of fullerenes. Etymology The discoverers of the allotrope named the newfound molecule after American architect R. Buckminster Fuller, who designed many geodesic dome structures that look similar to and who had died in 1983, the year before discovery. ==Synthesis==

Soot is produced by laser ablation of graphite or pyrolysis of aromatic hydrocarbons. Fullerenes are extracted from the soot with organic solvents using a Soxhlet extractor. This step yields a solution containing up to 75% of , as well as other fullerenes. These fractions are separated using chromatography. Generally, the fullerenes are dissolved in a hydrocarbon or halogenated hydrocarbon and separated using alumina columns. Synthesis using the techniques of "classical organic chemistry" is possible, but not economic. ==Structure==

Buckminsterfullerene is a truncated icosahedron with 60 vertices, 32 faces (20 hexagons and 12 pentagons where no pentagons share a vertex), and 90 edges (60 edges between 5-membered & 6-membered rings and 30 edges are shared between 6-membered & 6-membered rings), with a carbon atom at the vertices of each polygon and a bond along each polygon edge. The van der Waals diameter of a molecule is about 1.01 nanometers (nm). The nucleus to nucleus diameter of a molecule is about 0.71 nm. The molecule has two bond lengths. The 6:6 ring bonds (between two hexagons) can be considered "double bonds" and are shorter than the 6:5 bonds (between a hexagon and a pentagon). Its average bond length is 0.14 nm. Each carbon atom in the structure is bonded covalently with 3 others. A carbon atom in the can be substituted by a nitrogen or boron atom yielding a or respectively. ==Properties==

For a time buckminsterfullerene was the largest known molecule observed to exhibit wave–particle duality. In 2020 the dye molecule phthalocyanine exhibited the duality that is more famously attributed to light, electrons and other small particles and molecules. Solution Fullerenes are sparingly soluble in aromatic solvents and carbon disulfide, but insoluble in water. Solutions of pure have a deep purple color which leaves a brown residue upon evaporation. The reason for this color change is the relatively narrow energy width of the band of molecular levels responsible for green light absorption by individual molecules. Thus individual molecules transmit some blue and red light resulting in a purple color. Upon drying, intermolecular interaction results in the overlap and broadening of the energy bands, thereby eliminating the blue light transmittance and causing the purple to brown color change. Solid In solid buckminsterfullerene, the molecules adopt the fcc (face-centered cubic) motif. They start rotating at about −20 °C. This change is associated with a first-order phase transition to an fcc structure and a small, yet abrupt increase in the lattice constant from 1.411 to 1.4154 nm. solid is as soft as graphite, but when compressed to less than 70% of its volume it transforms into a superhard form of diamond (see aggregated diamond nanorod). films and solution have strong non-linear optical properties; in particular, their optical absorption increases with light intensity (saturable absorption). forms a brownish solid with an optical absorption threshold at ≈1.6 eV. It is an n-type semiconductor with a low activation energy of 0.1–0.3 eV; this conductivity is attributed to intrinsic or oxygen-related defects. Fcc contains voids at its octahedral and tetrahedral sites which are sufficiently large (0.6 and 0.2 nm respectively) to accommodate impurity atoms. When alkali metals are doped into these voids, converts from a semiconductor into a conductor or even superconductor. ==Chemical reactions and properties==

undergoes six reversible, one-electron reductions, ultimately generating . Its oxidation is irreversible. The first reduction occurs at ≈−1.0 V (Fc/), showing that is a reluctant electron acceptor. tends to avoid having double bonds in the pentagonal rings, which makes electron delocalization poor, and results in not being "superaromatic". behaves like an electron deficient alkene. For example, it reacts with some nucleophiles. Halogenation Addition of fluorine, chlorine, and bromine occurs for . Fluorine atoms are small enough for a 1,2-addition, while and add to remote C atoms due to steric factors. For example, in and , the Br atoms are in 1,3- or 1,4-positions with respect to each other. Under various conditions a vast number of halogenated derivatives of can be produced, some with an extraordinary selectivity on one or two isomers over the other possible ones. Addition of fluorine and chlorine usually results in a flattening of the framework into a drum-shaped molecule. Metal complexes forms complexes akin to the more common alkenes. Complexes have been reported molybdenum, tungsten, platinum, palladium, iridium, and titanium. The pentacarbonyl species are produced by photochemical reactions. : {{chem2|M(CO)6 + C60 → M(\h{2}C60)(CO)5 + CO}} (M = Mo, W) In the case of platinum complex, the labile ethylene ligand is the leaving group in a thermal reaction: : {{chem2|Pt(\h{2}C2H4)(PPh3)2 + C60 → Pt(\h{2}C60)(PPh3)2 + C2H4}} Titanocene complexes have also been reported: : {{chem2|(\h{5}Cp)2Ti(\h{2}(CH3)3SiC≡CSi(CH3)3) + C60 → (\h{5}Cp)2Ti(\h{2}C60) + (CH3)3SiC≡CSi(CH3)3}} Coordinatively unsaturated precursors, such as Vaska's complex, for adducts with : : {{chem2|trans\-Ir(CO)Cl(PPh3)2 + C60 → Ir(CO)Cl(\h{2}C60)(PPh3)2}} One such iridium complex, {{chem2|[Ir(\h{2}C60)(CO)Cl(Ph2CH2C6H4OCH2Ph)2]}} has been prepared where the metal center projects two electron-rich 'arms' that embrace the guest. Endohedral fullerenes Metal atoms or certain small molecules such as and noble gas can be encapsulated inside the cage. These endohedral fullerenes are usually synthesized by doping in the metal atoms in an arc reactor or by laser evaporation. These methods gives low yields of endohedral fullerenes, and a better method involves the opening of the cage, packing in the atoms or molecules, and closing the opening using certain organic reactions. This method, however, is still immature and only a few species have been synthesized this way. Endohedral fullerenes show distinct and intriguing chemical properties that can be completely different from the encapsulated atom or molecule, as well as the fullerene itself. The encapsulated atoms have been shown to perform circular motions inside the cage, and their motion has been followed using NMR spectroscopy. ==Potential applications==

In technology The optical absorption properties of match the solar spectrum in a way that suggests that -based films could be useful for photovoltaic applications. Because of its high electronic affinity it is one of the most common electron acceptors used in donor/acceptor based solar cells. Conversion efficiencies up to 5.7% have been reported in –polymer cells. In health Ingestion and risks is sensitive to light, Otherwise, a study found that remains in the body for a longer time than usual, especially in the liver, where it tends to be accumulated, and therefore has the potential to induce detrimental health effects. Oils with C60 and risks An experiment in 2011–2012 administered a solution of in olive oil to rats, achieving a 90% prolongation of their lifespan. in olive oil administered to beagle dogs resulted in a large reduction of C-reactive protein, which is commonly elevated in cardiovascular disease and cerebrovascular disease. Many oils with have been sold as antioxidant products, but it does not avoid the problem of their sensitivity to light, that can turn them toxic. A later research confirmed that exposure to light degrades solutions of in oil, making it toxic and leading to a "massive" increase of the risk of developing cancer (tumors) after its consumption. To avoid the degradation by effect of light, oils must be made in very dark environments, encased into bottles of great opacity, and kept in darkness, consumed under low light conditions and accompanied by labels to warn about the dangers of light for . Some producers have been able to dissolve in water to avoid possible problems with oils, but that would not protect from light, so the same cautions are needed. ==References==